The present invention relates to a seat belt system for motor vehicles which are of the type having a seat belt windable onto and retractable from a seat belt winding roller fixedly connected to the motor vehicle and extending to and through a connecting tongue which is releasably couplable to an end fixture fixedly connected to the vehicle, whereby an electrical lead extends along at least a portion of the seat belt.
In particular, in connection with the operation of a seat belt system in cooperation with an airbag apparatus and/or with a force limiting device, efforts are made to capture or determine the information concerning the tension arising in a deployed or loaded seat belt due to the application thereonto of a pulling force, in order to draw therefrom conclusions concerning the control of the operation of the airbag apparatus and/or of the force limiting device. For example, as is disclosed in DE 43 26 198 A1, a seat belt windup roller is intermediately connected to a force measuring cell which acts as a tension detector. With such a device, which comprises an external measurement apparatus, the output is imprecise and, at the same time, the device can only be installed and adjusted with considerable effort.
The present invention offers a solution to the challenge of providing a seat belt system that provides an immediate or instant measurement of the pulling force applied to the textile seat belt without the need for an intermediate activation of an external measuring apparatus.
The present invention thus makes use of a conventionally known arrangement of an electrical lead in a textile seat belt, as is shown, for example, in the arrangement disclosed in EP 0 830 994 A1; in this known seat belt security system, an electrical lead is integrated into the seat belt to serve as an antenna and, to this extent, is a component of a code capturing unit in an anti-theft system, in that the antenna arranged in the seat belt receives a code signal provided by a person having permission to occupy the vehicle and transmits the signal to an evaluation unit. It is not possible, however, to employ such an arrangement for the transmission of a signal indicating the pulling force on a seat belt.
The present invention provides, in further details thereof, an electric conductor extending along a seat belt, which has been unwound from a seat belt roller, and connectable to an electric supply source. A further aspect of the present invention is a measurement device for measuring the variation in the electrical properties of the electrical lead, which change as a function of the extension of the seat belt and are produced due to the application of force on the seat belt and the present invention includes. In yet a further aspect thereof, an evaluation device is provided for transforming the signal transmitted thereto by the measurement device into the respective seat belt force value. The present invention provides the advantage that the one or several conductors formed into the seat belt permit an instantaneous transmission of measurement signals, which are correspondingly received in suitable measurement devices and provided to a thereafter actuated evaluation device for conversion into the respective seat belt force values. A capture and transformation of the measurement signals in this manner is, for example, known in connection with the deployment of strain measurement bands as a basic concept.
In accordance with one embodiment of the present invention, it is provided that the electrical lead is woven into the seat belt. In an arrangement of this type, the electrical lead must possess the same or, at least, similar mechanical properties as the textile material such as, preferably, a reduced modulus of elasticity.
In accordance with a first embodiment of the present invention, it can be provided that the electrical connection is arranged with several leads extending in the direction of the elongate or longitudinal axis of the seat belt and organized into lead bands; in this embodiment of the present invention, the changes in the electrical resistance in the electrical leads or, respectively, the individual lead bands, which occur as a function of the extension of the seat belt, are sensed.
In another embodiment of the present invention, it is provided that the electrical lead is configured in a meandering or serpentine configuration extending transversely to the longitudinal axis of the seat belt and arranged in lead bands. Upon the application of an electrical current in such an electrical lead configuration, an annular magnetic field is formed around the individual lead bands, which penetrates through the lead loops in an opposite direction. In connection with the extension of the seat belt due to the application of a pulling or tensioning force, corresponding relative movement between the individual lead loops induces a voltage potential in the electrical leads and this voltage variation can be sensed as a variation in the electrical resistance; it is, however, also possible to instantly detect the variation of the magnetic field by, for example, a Hall sensor and to transmit immediately a signal representative of the extension of the seat belt.
In accordance with another embodiment of the present invention, it can be provided that one electrical lead extends on the seat belt along the longitudinal axis thereof and another electrical lead extends in serpentine manner transverse to the longitudinal axis of the seat belt, with the one electrical lead and the other electrical lead overlying one another and two measurement apparatus are provided for measuring the respective signals provided from the two electrical leads. An arrangement such as this makes possible, in addition, a determination of the length of the withdrawn seat belt or, respectively, a determination of the rate of unwinding or extension of the seat belt, as is further provided in another aspect of an embodiment of the present invention, in that the length of the unwound seat belt can be measured by a count of the loops of the electrical lead passing by a counting location, whereupon this counting result can be factored together with a consideration of the elapsed time of the seat belt unwinding movement to yield, as well, a determination of the rate of unwinding of the seat belt.
In accordance with one embodiment of the present invention, it is provided that a supply electrical lead, which is connected to a voltage supply, is configured on the seat belt and a sensor lead separate from the supply lead is arranged as well on the seat belt, whereby the measurement apparatus is connectable to the sensor lead. In this connection, an electrical voltage potential is applied to the supply electrical lead, which produces a corresponding magnetic field. Consequently, an extension of the seat belt produces relative movement between the supply lead and the sensor lead and thereby induces a voltage potential in the sensor lead which is sensed by corresponding sensors. It can also be imagined that the capacitance between the supply lead and the sensor lead can be measured or captured, as the capacitance reduces in correspondence with the increasing distance between the supply lead and the sensor lead which occurs as the seat belt is further extended.
As the electrical lead bands are preferably continuously formed in the seat belt web during its manufacture, the individual electrical lead bands must, following the layout of the seat belt, be configured into closed electrical current loops with one another and, in connection with an aspect of one embodiment of the present invention, it is provided that this connection between the electrical lead bands is provided by a bridging clip on the seat belt.
In connection with one embodiment of the present invention, it is provided that the seat belt is formed of a web comprised of fibers having electrical connecting or conducting properties.
In accordance with an embodiment of the present invention, it is provided that the electrical energy supply of the electrical leads is accomplished in a wireless manner via an electrical supply winding which encircles the seat belt.
In connection with the configuration of the measurement device in one embodiment of the present invention, it is provided that the measurement device comprises a contact located at a fixed location fastening point of the seat belt; such contacts can be arranged especially in the region of the securement of the seat belt on the shaft or pin of the seat belt winding roller as well as at the vehicle fixed connection end fixture.
In another embodiment of the present invention, the measurement device includes sensors which are arranged out of contact with the seat belt, whereby, in accordance with the respective layout and arrangement of the electrical lead or, respectively, the electrical lead bands, the sensors are configured as inductive sensors, magnetic sensitive sensors, or Hall sensors. It can further be provided that the sensors capture capacitance measurements.